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Achieving higher brightness of a single-photon emitter (SPE) is central for advanced applications from quantum information processing to quantum sensing. However, most approaches of integrating quantum emitters and photonic resonators require accurately localizing the emitter into a photonic structure, which is a challenge. Here, we report using dielectric microspheres for laser focusing to create SPEs in hexagonal boron nitride and in situ enhance the emission via photonic coupling between the SPE and the dielectric microspheres. The photoluminescence intensity is increased by 2.4-fold, achieving a high brightness SPE with a saturation intensity of up to 19.6 Mcounts s−1. This approach provides a feasible way to generate a high-performance SPE while simultaneously enabling precise coupling of the quantum light source and optical resonators. [ABSTRACT FROM AUTHOR]

Nitrogen-vacancy (NV) color centers in diamonds with narrow optical linewidths are commonly used as solid-state single-photon sources that emit indistinguishable photons. However, NV color centers prepared using ion implantation typically have large optical linewidths of over 100 MHz. Herein, we used the femtosecond laser direct writing (FsLDW) technique to prepare single NV color centers in diamond with a narrow optical linewidth of 13.05 ± 0.2 MHz and a long decoherence time of 445 ± 27.6 μs. In addition, the density functional theory was adopted to establish calculation models and illustrate why single NV color centers prepared by FsLDW have narrower linewidths compared to those of the ion implantation method. Thus, this study provides an effective reference for the preparation of narrow-linewidth single-color centers in diamonds and other wide-gap crystals. [ABSTRACT FROM AUTHOR]

First-principles calculations reveal a Mexican-hat potential energy surface (PES) for two-dimensional (2D) In2Se3. This unique PES leads to a pseudo-centrosymmetric paraelectric β phase that resolves the current controversy between theory and experiment. We further show that while the α-to-β (ferroelectric-to-paraelectric) phase transition is fast and coherent, assisted by an in-plane shear phonon mode, a random distribution of the atoms in the trough of the PES acts as an entropy barrier against the reverse β-to-α transition. This will be the origin of the speed limitation of current In2Se3 ferroelectric devices. However, if one orders the β phase (due to the formation of in-plane ferroelectric domains), the reverse transition can take place within tens of picoseconds in the presence of a perpendicular electric field. Finally, the Mexican-hat PES is a general feature for the entire family of 2D III2-VI3 materials. Our finding offers a critical physical picture in controlling the ultrafast reversible phase transition in 2D In2Se3 and other III2-VI3 materials, which will benefit their practical industrial development for advanced ferroelectric devices. [ABSTRACT FROM AUTHOR]

Organic single crystals are highly promising for applications in optoelectronic devices because of their higher mobility and thermal stability than amorphous thin films. Although white organic single crystals have been fabricated by the double-doped method and applied to realize white organic light‐emitting devices (WOLEDs), the unbalanced carrier transport properties of the unipolar crystals severely limit the device performance. Here, ambipolar white organic single crystals are obtained by using mixed p- and n-type molecules as an ambipolar host for the red and green dopants. The white crystal with balanced carrier transport and balanced blue, green, and red emission intensity was applied to the single-crystal WOLEDs. The highest brightness of 1956 cd m−2 and the current efficiency of 1.31 cd A−1 are achieved, which are the best performance of the single-crystal WOLEDs reported to date. A high color rendering index is obtained, which varies between 82 and 87 with increasing driving current. It is expectable that this strategy would support the practical applications of organic single crystal-based OLEDs. [ABSTRACT FROM AUTHOR]

In recent years, orbital angular momentum (OAM) beams and their generation methods have drawn increasing interest. Generating multiple OAMs in a three-dimensional space simply and efficiently is meaningful and challenging. Herein, we proposed an integrated multi-OAM generator based on the independent controlling phase division. Realized through the two-photon additive manufacturing, the device possesses a continuous surface with a diameter of 100 μm. Using the generator, arbitrary OAM modes were demonstrated, including the axial position, the number of topological charges, and the direction of rotation. The unique optical characteristics were mutually verified experimentally and through simulation. Vortex beams carrying multiple OAMs will provide more degrees of freedom to manipulate light for exciting applications such as optical communications, micromanipulation, and quantum optics. [ABSTRACT FROM AUTHOR]